Potterton Netaheat Electronic won't fire up?

Hi all,
A while ago some might remember me mentioning here that an elderly neighbour we keep an eye on was finding heating on when she only wanted hot water. I believe the diagnosis was the rubber ball in the motorised valve was allowing water past into the CH cct when in the HW position and I bought a new valve ready.
She was happy to just use immersion for HW so I thought we'd wait till it was a little bit cooler in the loft and in general before doing the job.
She mentioned to the Mrs earlier that it was starting to get a bit cooler and so I just popped over to swap her back to the gas boiler and re-set the timer to get things flowing again and whilst it looks and sounds like it's trying to spark up, it's not managing to?
We have the water pump running (checked via the spindle cover), the boiler fan, the igniter bit it looks like it might fire up a pilot > flame failure detector > main burner but isn't getting the pilot, if that's actually what happens. If it should light the main burner directly from the igniter it's not doing that either. [1]
I can't smell any gas on the outside but I can feel reasonable airflow.
Turn the main boiler knob to off, leave it a few seconds, turn it back on again, and you hear the fan come on, then after a few seconds delay, a fairly loud 'clunk' (gas valve?) and then the igniter starts going but that's it? She has gas on the hob nearby.
Anyone had / got one and can remember the fire up sequence or can offer any other thoughts please?
I've swapped her back to the immersion heater for tonight and can have a closer look in the morning.
Cheers, T i m
[1] If you peer into the boiler though the spy hole and watch carefully, every 3 or 4 sparks it looks like it is surrounded by a tiny flame but as if it's blown out before it can build up?
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snipped-for-privacy@spaced.me.uk says...

Mine has exhibited these symptoms. Here's what I do to mine. Isolate from electricity. Pull off the thermostat knob. Remove a 'rubber' bung to reveal a screw which holds on the control gear front cover. Remove the screw (mine is captive)and the cover. There is a clear plastic tube which passes through the steel backplate close to the spark generator black box. It goes into a pressure switch (a disk about 75mm dia). Where it passes through the backplate, the plastic tube is jointed by what looks like a bit of brass tubing. But this is a restrictor, with a very tiny hole in it. Pull the clear plastic tubes off it and blow it out, or carefully probe with a fine needle. Job done, I do it routinely about every 5 years. You can test if the boiler starts by turning on the electricity, there will be live terminals exposed, and sucking on the tube that goes to the pressure switch. Re-assemble. Hope this fixes it.
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wrote:
<snip> >> [1] If you peer into the boiler though the spy hole and watch

I have been in there a while back when fitting a replacement controller PCB so that sounds familiar. ;-)

Sounds familiar.

I think I may have a 'pricker' somewhere but she might also have a good range of needles if I can't find it.

Fingers crossed then. ;-)

Understood.

Reverse of ...

Me too.
So, is it simply the fact that something doesn't think the fan is running and pulling a sufficient vacuum on that side of the boiler to turn on the main gas valve?
Cheers, T i m
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On 09/10/2019 20:00, T i m wrote:

Going off at a tangent... Beware of any activity which requires removing the case.
https://www.gassaferegister.co.uk/media/2010/tb-006-industry-guidance-checking-seals-on-rs-positive-pressure-appliance-cases.pdf
"... there is a risk that products of combustion may escape into the rooms pace... ... A list of these types of appliances is contained in Appendix 1"
Appendix 1 has a number of Potterton Netaheat Electronic products...
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wrote: <snip> >> [1] If you peer into the boiler though the spy hole and watch

Please do. ;-)

Handy, thanks.

Noted (thanks).
Everything I've done on it so far is outside of the sealed case so that's ok.
I checked the restrictor mentioned by Mike elsewhere and whilst I can't say it was blocked, even after being pricked out and clear when held up to the light, it was still quite restrictive to being blown though (but on a par for the size of the hole).
Lightly sucking on the pipe caused the microswitch to 'click' so I put the hoses back on and it did then fire up (see below).
I seemed to go though the same sequence (sat their sparking for maybe 30 seconds) but then fired up. I'm not sure if there was actually a partial blockage in the pressure detector system or that I didn't leave it long enough previously or just coincidence / something else but it now seems to fire up ok, albeit after what seems like quite a while trying.
As an aside, the front of the case seems to get quite hot (you can't quite hold your hand on it), and smells a bit hot. maybe because it's not been on for a few months or because it was working quite hard bringing everything up to temp?
Anyway, whilst checking stuff out I noticed that the motorised valve wasn't returning (by spring) to the un-powered position, even when the head was removed, but would if you gave the motor gear a nudge?
Considering how old it all must be, maybe a complete new MV head (V4073A1039) might be in order to go with the replacement valve?
Cheers, T i m
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On 10/10/2019 16:02, T i m wrote:

I've just replaced a Netaheat Electronic 16/22 and have a fully working electronics board which I was just about to put on eBay.
From memory you would hear the fan start, then the clunk, the faintly the clicking of the igniter spark, then the whooomph as the burners lit and another clunk. Sometimes it could be a long time till it lit but probably only 30secs or so. It just felt like forever. The case did get hot when it had been on a long time but not too hot to touch but really quite hot.
Mine was 31yrs old when I replaced it last month. Replacement WB Greenstar is almost silent in comparison (outside flue is noisier than the old one). Difference in performance with a system boiler and pressurised system is night and day. The Netaheat had 2 replacement boards in the time I've been here, last one was in 2011. Also it wouldn't light once and it turned out there was water/condensation in the gas pipes. Only issues in 19years of use driving a hot water tank and 14 rads in Sunnny Scotland.
I wonder if the WB will last 31 years?
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<snip>

What do they go for OOI?

Sounds familiar. ;-)

Thanks and it does eh.

This one seems to get particularly hot on the lower half at the front, but knowing where the burners are that probably makes sense.

I think I have repaired one for her (dryjoint) and then a couple of years later, replaced it with a second hand one.

Oh?

And that of course is the question around the 'bigger picture'.
If the old boiler was not particularly efficient but cost little in the way of replacement components and people driving miles in diesel vans to repair it, I wonder how that might compare carbon footprint wise with something supposedly 'greener' but possibly more complex and so less reliable?
Thanks for the feedback. ;-)
Cheers, T i m
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On 11/10/2019 09:55, T i m wrote:

On eBay for secondhand as seen inc P&p, less than £50. Secondhand but with guarantee inc p&p, I've seen upto £125 asked for them.
I believe the gas valves are no longer available new. There may well be plenty of used spares about however. I'm not sure what the legal and/or of safety implications are in fitting secondhand gas valves. Fans and seals etc. are available still.
In my case I'd put off replacing it for far too long and hearing of the gas valve situation, I finally cracked my wallet open!
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On Thu, 10 Oct 2019 16:02:21 +0100, T i m wrote:
<snip>

<snip>

Just reminded me that with our old (ancient) boiler everything was fine apart from the thermocouple needing replacing now and then, and the pilot light gas jet getting blocked now and then. As far as I can tell there was a bit of dust/dirt in the gas feed which occasionally blocked the pilot light. A quick clean - poke and blow - and all was well for another year or so.
So there could just be a little dust in the piping which blocks the pilot light now and then.
Cheers
Dave R
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I've just replaced the valve body on the motorised valve serving the upstairs zone in my house. It was extremely stiff to turn even with the head off and a pair of pliers on the shaft. It wasn't worth the aggravation of trying to remove the spindle to investigate and possibly clean and lubricate with a risk the shaft seal would leak afterwards. Fortunately I had installed gate valves either side in the pipework when I first put the system in so it was a few minutes work and no drain down required.
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